Method of briquetting solid fuels



United States Patent 3,001,856 METHOD OF BRIQUETTING SOLID FUELS Wilhelm Reerink, 2 Ruttleskamp, Essen-Bredeney, Germany, Walter Muschenborn, 39 Elfriedenstrasse, Essen,

Germany, and Erich Notzold, 36 Ehrenaue, Essen- Haarzopf, Germany N0 Drawing. Filed Nov. 30, 1956, Ser. No. 631,987

4 Claims. (Cl. 4423) This invention relates to the briquetting of solid fuels, particularly mineral coal, utilizing the bituminous binders hitherto customary for this purpose such as mineral coal tar pitch, hard bitumen from the petroleum industry, suitable asphalts or the like.

In briquetting methods hither-to customary, in which the binder is added in a finely ground state to the coal to be briquetted, and the mixture thereupon heated to a temperature above the softening'point of the binder used and then pressed, a comparatively high addition of binder, which in the case of ground mineral coal tar pitch amounts to at least 6 percent, and generally more, is necessary in order to obtain perfect, particularly rubbing-resistant briquettes.

The cost of production of the briquettes is thus very unfavorably influenced on account of the relatively high price of mineral coal tar pitch, which amounts to over Ib9 per metric ton. In addition, the necessary amounts of mineral coal tar pitch, of which only relatively small amounts are produced in the coking of mineral coal, are difiicult to obtain.

Numerous proposals have already been made for the purpose of reducing the consumption of binder required for briquetting. Attempts to achieve this purpose by raising the mixing temperature have, however, not led to satisfactory results because limitations are entailed by the fact that the mixing temperature cannot normally be increased beyond 100 C., on account of the water content of the material to be briquetted, which amounts to a few percent and is practically always present.

Instead of mineral coal tar pitch, which has a relatively high melting point, it has further been proposed to use binders having a lower softening point, and which accordingly are of lower viscosity at the attainable operating temperatures than this normal briquetting pitch. This step, which in itself leads to a certain degree of success, is however applicable, for economic reasons, only to new installations, because the conversion to soft pitch of a briquetting factory working with mineral coal tar pitch and which is equipped with installations for the comminution and admixture of this readily grindable briquetting pitch melting at high temperature, is a very considerable undertaking.

A further disadvantage in the use of soft pitches arises from the fact that, because they cannot be ground, they can be used only in the molten condition and must therefore be stored in heated containers and be transported by means of heated pumps and pipes.

r In contradistinction thereto, the present invention provides a briquetting process which, while making use of the usual binders, that is to say particularly mineral coal tar pitch, enables the amount of binder required to be considerably reduced, while at the same time further advantages are gained not only in respect of the quality of the briquettes to be produced but also in respect of the reduction of the cost of the entire process. The application of the new process is furthermore not restricted to the use of mineral coal tar pitch but by suitable adaption can also be applied to the use of other hard binders, such as hard bitumen, natural asphalts and the like having a softening point above 70 C.

The method according to the invention broadly comprises first wetting the coal to be briquetted with an oil in which the bituminous binder issoluble, such as mineral oil, coal tar oil, hydrocarbon fuel oil and the like, before the coal is mixed with the binder.

The briquetting coal treated in this manner, the particles of which are thus coated with a thinfilm of oil, can be particularly well briquetted after being mixed with the ground briquetti-ng pitch, heated and mixed in the kneading mill, because during this treatment the briquetting pitch is partly dissolved in the oil film adhering to the particles of coal. The same result is thus obtained in this respect as when using soft pitches, that is to say pitches having a higher oil content, as binders.

In accordance with a further and very important feature of the invention, the method is preferably carried out by subjecting only a part of the coal to be briquetted, having the usual grain size of up to 6 or eventually 8 mm., to the preceding wetting treatment with oil, whereupon the normal briquetting coal not having undergone pretreatment is mixed with'this oil-wetted fraction. Eventually the part of the initial coal subjected to the oil treatment may be the coal dust separated therefrom and being in the order of grain size of up to 1 mm. Otherwise, comminution of the coarser particles may be combined with the oil treatment.

The wetting treatment, namely the uniform and effective distribution of the relatively small amount of oil over the surface of the particles of coal, is facilitated if, as a further development of the new method, it is carried out in the presence of water or water vapor.

The present process may be advantageously combined with the method which is the subject of an earlier pro posal by us, Serial No. 235,132, filed November 6, 1951, now US. Patent 2,769,537, the disclosure of which is hereby incorporated herein by reference. According to this earlier proposal, ash and water are removed from very fine coal or coal sludge by intimately mixing the water-containing raw material, reduced to a very grain state or already existing in that state, with suitable oils and the like, until surface wetting has been achieved, and at the same time simultaneously dispersing the raw material in water, whereafter the dispersion is separated by mechanical means and with simultaneous dewatering of the concentrate into oil-coated fine grain coal and waste water-containing waste solids. By this process, the water on the coal particles is replaced by an oil film. The oil wetting treatment is preferably carried out by treating the mixture in a Pallman baffie plate mill or kneading mill under conditions by which the mixture is exposed to turbulence effects and/ or changing pressure stresses, and the separation of the resulting dispersion with simultaneous extraction of water takes place by means of a centrifugal screen or the like. This Pallman baffle plate mill, which is described in detail in said aforementioned application Serial No. 255,132, consists of two co-axially disposed circular bafile plates, at least one of which rotates, the peripheral surfaces of the plates closely adjoining each other to provide a narrow gap through which the material is ejected.

The clean, oil-wetted coal obtained by this treatment can, within the framework of the new method, be added without intermediate drying directly to the remainder of the briquetting coal having the usual water content.

It has been ascertained that when using mineral coal tar pitch as binder, the amount of such binder required for this purpose can be reduced from the amount of 6 to 7% previously required to about 4%, while for the oil-wetting a proportionate amount of only /2 to 1% of the amount of the briquetting coal is necessary.

In the practical performance of the method, only a fraction to about 10 to 20% by weight of the entire briquetting coal of a grain size of -6, eventually 0-8 mm., is subjected to pretreatment with oils and thereupon it is mixed with the main fraction of the coal. The amount of oil employed to :form an oil film around each coal particle is 5% to by weight of the minor coal fraction which is oil treated in the first phase, which oil-wetted fraction is then added to the main coal fraction, along with binder, and then briquetted.

It is also possible and eventually especially advantageous to use as fraction to be oil wetted not a part divided of the entire coal to be briquetted, i.e. a part with the same grain size, but a very fine coal in the form of coal dust which may have been separated from the initial coal, or any coal slurry in a grain size of up to 1 mm. Then the machine in which the oil treatment takes place is released from the comminution work, and an otherwise not valuable material-coal dust or coal slurryis used in a very economical manner.

Example 1 From a 1,000 kg. supply of fine, comparatively dry coal having a grain size of 0 to 6 mm., and a water content of about 2%, 100 kg. were removed and to this fraction were added 10 l. of water and 10 kg. mineral oil. The resulting mixture was intensely mixed and passed through a Pallman baffle plate mill, leaving the mill in a comminuted state through the narrow circumferential gap between the relatively movable baffie plates. This mixture, now weighing 120 kg. was added to the 900 kg. of coal remaining in the initial supply, 50 kg. of coal tar pitch was then added to the mixture and the whole mass mixed and briquetted in a conventional manner. From this process, briquettes having a breaking index of 20.9 kg./cm. were obtained.

Example 2 To 100 kg. of a coal slurry with a grain size of below 1 mm. having a water content of 11% were added 4 kg. of normal fuel oil and the mixture subjected to a Pallman baffle plate mill to wet the individual coal particles with an oil film which replaces the Water film previously thereon, while simultaneously forming a flowable dispersion, which dispersion is thrown out through the peripheral narrow gap between the battle plates of the mill. The dispersion is then centrifuged to separate the water and the oil-coated coal. The thus characterised oil-coated coal was then added to 500 kg. fine coal of 0-6 mm. grain size of 7.6% ash content along with 21 kg. of coal tar pitch. This mixture was passed through mixing screws and then briquetted in a conventional manner.

The greater the amount of oil used, and the more completely the pitch is soluble in the respective oil, the greater will be the saving of briquetting pitch.

In the case of the use of other bituminous binders, such as hard bitumen and natural asphalts, which is also possible, oils which have a favorable dissolving power for the binders in question must be used for the pretreatment. Within the framework of the new method it is possible to use relatively cheap and low-grade oils, such as anthracene oil, aromatic fuel oil and also oils of high viscosity at normal temperatures, if in this case the pretreatment of the coal takes place at operating temperatures elevated so that a low viscosity state of these oils results.

Not only does the new method lead to a considerable reduction in briquetting costs, but the consequent possibility of combining briquetting directly with the preparation of coal having a high ash content results in a reduction of the cost and a simplification of the entire installation, and also makes it possible to use profitably as briquetting coal low-grade starting materials, such as coal sludges and coal dust after corresponding preparation treatment.

This application is a continuation in part of application Serial No. 379,724, filed September 11, 1953, entitled Method of Briquetting Solid Fuels, now abandoned.

What is claimed is:

1. A method of briquetting coal with a hard binder from the group consisting of coal tar pitch, hard bitumen and asphalt, which comprises separating an amount of the coal to be briquetted into a minor fraction not exceeding 20% of the whole and a major fraction, wetting said minor fraction with a mineral oil in which said hard binder is soluble and in quantity sufficient to cover the surface of the coal particles at least of said minor fraction, said oil film replacing the water film previously surrounding the particles of the minor fraction, while simultaneously dispersing the mixture in water to form a Howable dispersion by forcing the water-containing mixture through openings of narrow cross section, mechanically separating the resulting dispersion into oil-wetted coal fraction and ash-oontaining waste water, discarding the ash-containing waste water, mixing said oil-wetted fraction with the unwetted major fraction of the initial coal, mixing the whole with said hard binder being in the ground state, heating the mixture to a temperature above the softening point of said hard binder, and pressing the heated mixture to form briquettes.

2. A method of briquetting a solid fuel according to claim 1, characterised therein that the amount of oil used is sufficient to coat also the surface of the coal particles of the major fraction with oil.

3. A method of briquetting a solid fuel according to claim 1, characterised therein that the amount of oil used is about /2 to 1% of the entire solid fuel to be briquetted.

4. A method of briquetting coal with a hard binder from the group consisting of coal tar pitch, hard bitumen and asphalt, which comprises first subjecting a minor fraction of the coal not exceeding 20% of the coal to be briquetted, to a preliminary treatment consisting in intimately mixing said fraction with a mineral oil-containing substance in which the binder is soluble, to wet the individual coal particles with an oil film which replaces the water film previously thereon, while simultaneously dispersing the mixture in water to form a flowable dispersion by forcing the water-containing mixture through openings of narrow cross section, and thereafter mechanically separating the resulting dispersion into coal concentrate and waste water containing the ash in finely divided form, separating the coal concentrate and discarding said ash, admixing said coal concentrate with the remaining fraction of the coal, adding the binder to the coal mixture, and finally pressing the mixture to form briquettes.

References Cited in the file of this patent UNITED STATES PATENTS 1,895,056 Trent Jan. 24, 1933 2,556,154 Kern June 5, 1951 FOREIGN PATENTS 209,794 Great Britain J an. 22, 1924 510,095 Great Britain July 26, 1939 748,193 Great Britain Apr. 25, 1956 

1. A METHOD OF BRIQUETTING COAL WITH A HARD BINDER FROM THE GROUP CONSISTING OF COAL TAR PITCH, HARD BITUMEN AND ASPHALT, WHICH COMPRISES SEPARATING AN AMOUNT OF THE COAL TO BE BRIQUETTED INTO A MINOR FRACTION NOT EXCEEDING 20% OF THE WHOLE AND A MAJOR FRACTION, WETTING SAID MINOR FRACTION WITH A MINERAL OIL IN WHICH SAID HARD BINDER IS SOLUBLE AND IN QUANTITY SUFFICIENT TO COVER THE SURFACE OF THE COAL PARTICLES AT LEAST OF SAID MINOR FRACTION, SAID OIL FILM REPLACING THE WATER FILM PREVIOUSLY SURROUNDING THE PARTICLES OF THE MINOR FRACTION, WHILE SIMULTANEOUSLY DISPERSING THE MIXTURE IN WATER TO FORM A FLOWABLE DISPERSION BY FORCING THE WATER-CONTAINING MIXTURE THROUGH OPENINGS OF NARROW CROSS SECTION, MECHANICALLY SEPARATING THE RESULTING DISPERSION INTO OIL-WETTED COAL FRACTION AND ASH-CONTAINING WASTE WATER, DISCARDING THE ASH-CONTAINING WASTE WATER, MIXING SAID OIL-WETTED FRACTION WITH THE UNWETTED MAJOR FRACTION OF THE INITIAL COAL, MIXING THE WHOLE WITH SAID HARD BINDER BEING IN THE GROUND STATE, HEATING THE MIXTURE TO A TEMPERATURE ABOVE THE SOFTENING POINT OF SAID HARD BINDER, AND PRESSING THE HEATED MIXTURE TO FORM BRIQUETTES. 